The main state of the art is summarized in patent document PCT 2005000228, which is the only known document which attempts to solve this problem in this manner.
Communication, spectral analysis, RADAR and SONAR systems transmit a signal which reaches the receiver, whether reflected or not, after traversing a transmission medium. This medium behaves like a linear filter with a frequency H (ω) or temporal h[n] response to the impulse. It is necessary in most communication systems to eliminate the effects produced by the transmission medium on the emitted signal s[n] to enable the process of recovering the emitted information. This process is known as equalization. The frequency response can also be used to perform an analysis especially of the medium and thus obtain information about the physical properties thereof.
The channel acts like a filter and distorts the signal. Noise, n[n], due to disturbances in the channel, thermal noise or other signals interfering with the emitted signals must be added to this. In conclusion, the received signal, r[n], can be modeled as:r[n]=s[n]*h[n]+n[n]  (1)wherein * represents the convolution operation. A filter with impulse response, f[n], is necessary to eliminate the distortion introduced by the medium in the signal, such that:r[n]*f[n]≈s[n]  (2)
However, as the method is herein used, the time of calculating the filter coefficients is high and partially conditions the application of the system.